1. Field of the Invention
This invention relates to hydraulic dampers of the cylinder-and-piston type used for controlling the lag-lead movements of helicopter blades, and particularly to means for accurately indicating when a high pressure seal on the piston rod of the damper has become worn and is leaking oil excessively.
2. Description of the Prior Art
Dual seals have been used on the shafts of dampers and servomotors, with fluid pressure indicators connected to the area between seals to indicate leakage past the primary seal. U.S. Pat. No. 1,943,578 issued Jan. 16, 1934 to G. E. Bigelow shows such an arrangement applied to a high pressure centrifugal pump shaft. The area between the seals is connected to a conduit containing a restriction (valve) to a low pressure fluid system and a pressure gage is connected to the conduit between the restriction and the seals.
A disadvantage of this prior art structure is that a pressure built up in the return line for the leaked fluid, thereby giving a false indication of excessive leakage. This is particularly troublesome where the leaked-fluid line discharges into a fluid return system which is connected to other hydraulic devices as for example a helicopter rotor head which has a plurality of dampers operating concurrently.